The idea is, anything that want to speak to you, should use this plugin. That way, media and voice won't be used at the same time. NVoiceSynth keeps track of the player state and pauses it when it needs to say something.

you can have your app speak to nghost via nghost-cmd:

Code:

nghost-cmd nvoicesynth:null speak \"say something\"

LinuxICE beta2 will have this fix and Navit will be preconfigured to use nghost's voice synth engine for directions.